Electrode for lithium-ion cell, lithium-ion cell, and method for manufacturing electrode for lithium-ion cell

ABSTRACT

The present invention aims to provide an electrode for lithium ion batteries which exhibits excellent electrical conductivity even if its thickness is large. The electrode for lithium ion batteries of the present invention includes a first main surface to be located adjacent to a separator of a lithium ion battery and a second main surface to be located adjacent to a current collector of the lithium ion battery. The electrode has a thickness of 150 to 5000 μm. The electrode contains, between the first main surface and the second main surface, a conductive member (A) made of an electronically conductive material and a large number of active material particles (B). At least part of the conductive member (A) forms a conductive path that electrically connects the first main surface to the second main surface. The conductive path is in contact with the active material particles (B) around the conductive path.

TECHNICAL FIELD

The present invention relates to an electrode for lithium ion batteries,a lithium ion battery, and a method of producing an electrode forlithium ion batteries.

BACKGROUND ART

Reduction in carbon dioxide emissions has been strongly desired inrecent years for environmental protection. The automotive industry hasplaced great expectations on the introduction of electric vehicles (EVs)or hybrid electric vehicles (HEVs) to reduce carbon dioxide emissionsand has been extensively developing secondary batteries for driving themotors, the key to practical use of these vehicles. Secondary batteriesthat have received attention include lithium ion batteries, which havehigh energy density and high output power density.

A typical lithium ion secondary battery includes an electrode composedof a positive electrode current collector with a positive electrodeactive material applied thereto together with a binder and an electrodecomposed of a negative electrode current collector with a negativeelectrode active material applied thereto together with a binder. Abipolar battery includes a bipolar electrode composed of a currentcollector with a positive electrode layer on one side and a negativeelectrode layer on the other side. The positive electrode layer isformed by applying a positive electrode active material together with abinder to one side of the current collector. The negative electrodelayer is formed by applying a negative electrode active materialtogether with a binder to the other side (see Patent Literature 1, forexample).

In Patent Literature 1, paste for forming electrodes is applied at athickness of about 25 μm. Increasing the proportion of the positiveelectrode material and the negative electrode material in a battery isknown as a way to increase the energy density of the battery. PatentLiterature 2 discloses a method for increasing energy density of abattery, in which the film thickness of the electrodes is increased toreduce the relative proportion of the current collector and theseparator.

CITATION LIST Patent Literature

Patent Literature 1: JP 2011-86480 A

Patent Literature 2: JP H09-204936 A

SUMMARY OF INVENTION Technical Problem

As described in Patent Literature 2, increasing the film thickness of anelectrode reduces the relative proportion of the current collector andthe separator. This is considered effective for achieving higher batterycapacity.

However, in a bipolar electrode, increasing the electrode thicknessincreases the proportion of active materials located far from thecurrent collector. Since active materials themselves do not have highelectron conductivity, electrons will not smoothly move from such activematerials far from the current collector to the current collector. Thus,even if the amount of active materials become larger, simply increasingthe electrode thickness results in a higher proportion of activematerials that are less electronically conductive and not effectivelyused. As a result, the battery fails to have higher capacity despite theincreased electrode thickness.

As the active materials themselves do not have high electronconductivity, they have been blended with particulates such as acetyleneblack serving as a conductive additive to enhance the electronconductivity. However, in an electrode with an increased thickness, itis difficult for such a particulate conductive additive to exert theeffect of enhancing the electron conductivity.

Solution to Problem

The present inventors made intensive studies to solve the aboveproblems. They have found that excellent electron conductivity can beachieved, even in an electrode with an increased thickness, by forming aconductive path that electrically connects surfaces of the electrodealong the thickness direction of the electrode so that electronsgenerated from the active material can flow through the conductive pathto the current collector. The inventors thus arrived at the presentinvention.

The present invention relates to an electrode for lithium ion batteries,the electrode including a first main surface to be located adjacent to aseparator of a lithium ion battery and a second main surface to belocated adjacent to a current collector of the lithium ion battery,wherein the electrode has a thickness of 150 to 5000 μm, the electrodecontains, between the first main surface and the second main surface, aconductive member (A) made of an electronically conductive material anda large number of active material particles (B), at least part of theconductive member (A) forms a conductive path that electrically connectsthe first main surface to the second main surface, and the conductivepath is in contact with the active material particles (B) around theconductive path; a lithium ion battery including the electrode forlithium ion batteries of the present invention as at least one of anegative electrode and a positive electrode; a method of producing theelectrode for lithium ion batteries of the present invention, includingstep (P1) of providing a structure (Z) that contains the conductivemember (A), has voids therein, and has a first main surface and a secondmain surface, step (P2) of applying a slurry (X) containing the activematerial particles (B) to the first main surface or the second mainsurface of the structure (Z), and step (P3) of filling the voids in thestructure (Z) with the active material particles (B) by pressurizationor depressurization; a method of producing the electrode for lithium ionbatteries of the present invention, including step (Q1) of applying aslurry (Y) containing the conductive member (A) and the active materialparticles (B) to a film (E) and step (Q2) of fixing the active materialparticles (B) and the conductive member (A) onto the film (E) bypressurization or depressurization; a method of producing the electrodefor lithium ion batteries of the present invention, including step (T1)of applying a slurry (Y) containing the conductive member (A) and theactive material particles (B) to a current collector to form a slurrylayer on the current collector and step (T2) of disposing a separator onthe slurry layer and absorbing liquid from an upper surface of theseparator so as to fix the active material particles (B) and theconductive member (A) between the current collector and the separator;and a method of producing an electrode for lithium ion batteries, theelectrode including a first main surface to be located adjacent to aseparator of a lithium ion battery and a second main surface to belocated adjacent to a current collector of the lithium ion battery,wherein the electrode contains, between the first main surface and thesecond main surface, a conductive member (A) made of an electronicallyconductive material, a large number of active material particles (B),and a resin (F), at least part of the conductive member (A) forms aconductive path that electrically connects the first main surface to thesecond main surface, and the conductive path is in contact with theactive material particles (B) around the conductive path, the methodincluding step (R1) of hot-pressing a composition for an electrodecontaining the conductive member (A), the active material particles (B),and the resin (F) so as to fix the conductive member (A) and the activematerial particles (B) by the resin (F).

Advantageous Effects of Invention

The electrode for lithium ion batteries of the present inventionincludes, between the first main surface and the second main surface ofthe electrode, a conductive member made of an electronically conductivematerial. The conductive member forms a conductive path thatelectrically connects the first main surface to the second main surface,and thus electrons generated from the active material can flow throughthe conductive path to the current collector. Even if the electrode hasan increased thickness of 150 to 5000 μm and contains the activematerial in a relatively large amount, electrons from an active materialfar from the current collector smoothly reach the current collector. Theelectrode for lithium ion batteries of the present invention thus isexcellent in the electron conductivity and suitable for increasing thecapacity of a lithium ion battery.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view of an example of a structureof a lithium ion battery including the electrode for lithium ionbatteries according to the present invention as a positive electrode anda negative electrode.

FIG. 2 is a schematic cross-sectional view of only the positiveelectrode of the lithium ion battery illustrated in FIG. 1.

FIG. 3 is a schematic cross-sectional view of an example of anotherembodiment of the electrode for lithium ion batteries of the presentinvention.

FIG. 4 is a schematic cross-sectional view of an example of yet anotherembodiment of the electrode for lithium ion batteries of the presentinvention.

FIG. 5 is a schematic cross-sectional view of an example of yet anotherembodiment of the electrode for lithium ion batteries of the presentinvention.

FIG. 6 is a schematic cross-sectional view of an example of yet anotherembodiment of the electrode for lithium ion batteries of the presentinvention.

FIG. 7(a) and FIG. 7(b) schematically illustrates a step of fillingvoids in a structure with active material particles.

FIG. 8(a) and FIG. 8(b) schematically illustrates a step of fixingactive material particles and a conductive member onto a film.

FIG. 9(a), FIG. 9(b) and FIG. 9(c) schematically illustrates a step offixing active material particles and a conductive member between acurrent collector and separator.

FIG. 10(a) and FIG. 10(b) schematically illustrates a step of fixingactive material particles and a conductive member by a resin.

DESCRIPTION OF EMBODIMENTS

The present invention will be described in detail below.

The electrode for lithium ion batteries of the present inventionincludes a first main surface to be located adjacent to a separator of alithium ion battery and a second main surface to be located adjacent toa current collector of the lithium ion battery. The electrode has athickness of 150 to 5000 μm. The electrode contains, between the firstmain surface and the second main surface, a conductive member (A) madeof an electronically conductive material and a large number of activematerial particles (B). At least part of the conductive member (A) formsa conductive path that electrically connects the first main surface tothe second main surface. The conductive path is in contact with theactive material particles (B) around the conductive path.

In one embodiment of the electrode for lithium ion batteries of thepresent invention, the conductive member (A) includes conductive fibersconstituting a part of a nonwoven fabric. In another embodiment, theconductive member (A) includes conductive fibers constituting a part ofa woven fabric or a knitted fabric. In yet another embodiment, theconductive member (A) includes conductive fibers dispersed between thefirst main surface and the second main surface. In yet anotherembodiment, the conductive member (A) includes a resin provided withconductivity and constituting a part of foamed resin.

First, among the embodiments of the electrode for lithium ion batteriesof the present invention, the one in which the conductive member (A)includes conductive fibers constituting a part of a nonwoven fabric isdescribed below with reference to drawings.

FIG. 1 is a schematic cross-sectional view of an example of a structureof a lithium ion battery including the electrode for lithium ionbatteries according to the present invention as a positive electrode anda negative electrode.

A lithium ion battery 1 illustrated in FIG. 1 includes a positiveelectrode 10 and a negative electrode 20. A separator 30 is providedbetween the positive electrode 10 and the negative electrode 20.

A current collector 40 is provided on a surface of the positiveelectrode 10 opposite the separator 30. A current collector 50 isprovided on a surface of the negative electrode 20 opposite theseparator 30. In short, these components are stacked in the order ofcurrent collector 40-positive electrode 10-separator 30-negativeelectrode 20-current collector 50. They, in combination, form thelithium ion battery 1.

The electrode for lithium ion batteries of the present inventionincludes neither a separator nor a current collector. Each of thepositive electrode 10 and the negative electrode 20 illustrated in FIG.1 is the electrode for lithium ion batteries according to the presentinvention.

The positive electrode 10 is a sheet-form electrode having a specificthickness t1. The positive electrode 10 has a first main surface 11 thatis located adjacent to the separator 30 and a second main surface 12that is located adjacent to the current collector 40. The positiveelectrode 10 contains positive electrode active material particles 14.

Similar to the positive electrode 10, the negative electrode 20 is asheet-form electrode having a specific thickness t2. The negativeelectrode 20 has a first main surface 21 that is located adjacent to theseparator 30 and a second main surface 22 that is located adjacent tothe current collector 50. The negative electrode 20 contains negativeelectrode active material particles 24.

The thickness t1 of the positive electrode 10 and the thickness t2 ofthe negative electrode 20 are each 150 to 5000 μm. With such thickelectrodes, a battery can contain a large amount of active materials,which leads to a lithium ion battery with higher capacity.

The thickness t1 of the positive electrode for lithium ion batteriesaccording to the present invention is preferably 150 to 1500 μm, morepreferably 200 to 950 μm, still more preferably 250 to 900 μm.

The thickness t2 of the negative electrode for lithium ion batteriesaccording to the present invention is preferably 150 to 1500 μm, morepreferably 200 to 950 μm, still more preferably 250 to 900 μm.

Such a lithium ion battery including the electrode for lithium ionbatteries of the present invention as at least one of a negativeelectrode and a positive electrode is the lithium ion battery of thepresent invention.

Next, the electrode for lithium ion batteries of the present inventionis described.

FIG. 2 is a schematic cross-sectional view of only the positiveelectrode of the lithium ion battery illustrated in FIG. 1.

The positive electrode 10 has the first main surface 11 and the secondmain surface 12, as mentioned above. The positive electrode 10 contains,between the first main surface 11 and the second main surface 12,conductive fibers 13 as the conductive member (A) and positive electrodeactive material particles 14 as the active material particles (B).

In the embodiment illustrated in FIG. 2, the conductive member (A)includes conductive fibers 13 constituting a part of a nonwoven fabric.The nonwoven fabric has many voids. By filling the voids with the activematerial particles, the electrode for lithium ion batteries can beformed. Filling the voids with the active material particles will bedescribed in the section of the method of producing the electrode forlithium ion batteries of the present invention.

Part of the conductive fibers 13 has one end extending to the first mainsurface 11 and the other end extending to the second main surface 12. Inother words, at least part of the conductive fibers 13 forms aconductive path that electrically connects the first main surface 11 tothe second main surface 12.

A large number of conductive fibers 13 are intertwined with each otherbetween the first main surface 11 and the second main surface 12. Ifmultiple conductive fibers 13 are in contact with each other andcontinuously connect the first main surface 11 to the second mainsurface 12, the conductive fibers are also regarded as forming aconductive path that electrically connect the first main surface to thesecond main surface.

FIG. 2 shows examples of conductive fibers 13 corresponding toconductive paths that electrically connect the first main surface 11 tothe second main surface 12. Specifically, a conductive fiber 13 a showsan example of a single conductive fiber forming a conductive path. Twoconductive fibers 13 b show an example of conductive fibers being incontact with each other to form a conductive path.

Examples of the conductive fibers include carbon fibers such as PANcarbon fibers and pitch carbon fibers, conductive fibers containing ahighly conductive metal or graphite uniformly dispersed in syntheticfibers, metal fibers obtained by converting metals such as stainlesssteel into fibers, conductive fibers containing organic fibers whosesurface is coated with a metal, and conductive fibers containing organicfibers whose surface is coated with a resin containing a conductivesubstance. Among these conductive fibers, carbon fibers are preferred.

In the electrode of the present invention, if the conductive member (A)includes conductive fibers, the conductive fibers preferably have anelectrical conductivity of 50 mS/cm or more, more preferably 80 to 500mS/cm. The electrical conductivity of the conductive fibers can bedetermined by measuring the volume resistivity in accordance with JIS R7609 “Carbon fibre—Determination of volume resistivity” and calculatingthe reciprocal of the volume resistivity.

If the conductive fibers have an electrical conductivity of 50 mS/cm ormore, the conductive paths that are formed of the conductive fibers andconnect the first main surface to the second main surface have smallelectrical resistance. This advantageously enables smooth transfer ofelectrons from the active material far from the current collector.

The conductive fibers preferably have an average fiber diameter of 0.1to 20 μm, more preferably 0.5 to 2.0μ.

The fiber diameter of the conductive fibers is measured by SEMobservation. The average fiber diameter of the conductive fibers isdetermined as follows. Ten conductive fibers are randomly selected in a30-μm square field of view. The diameter at or near the middle of eachof the ten fibers is measured. This measurement is performed at threefields of view. The average of the diameters of a total of 30 fibers istaken as the measured value.

The conductive fibers may have any fiber length. The total fiber lengthof the conductive fibers per unit volume of the electrode is preferably10,000 to 50,000,000 cm/cm³, more preferably 20,000 to 50,000,000cm/cm³, still more preferably 1,000,000 to 10,000,000 cm/cm³.

The total fiber length of the conductive fibers per unit volume of theelectrode is calculated by the following formula.

(Total fiber length of conductive fibers per unit volume ofelectrode)=[(average fiber length of conductive fibers)×(weight ofconductive fibers used per unit volume of electrode)/(specific gravityof conductive fibers)]/[(unit area of electrode)×(electrode thickness)]

The average fiber length of the conductive fibers is measured by SEMobservation. Specifically, ten fibers are randomly selected in a 30-μmsquare field of view. The length of each of the ten fibers is measured.This measurement is performed at three fields of view. The average ofthe lengths of a total of 30 fibers is taken as the measured value ofthe average fiber length of the conductive fibers.

The positive electrode active material particles 14 are active materialparticles filling the voids in the nonwoven fabric. Examples of thepositive electrode active material particles include particles ofcomplex oxides of lithium and transition metals (e.g., LiCoO₂, LiNiO₂,LiMnO₂, LiMn₂O₄), particles of transition metal oxides (e.g., MnO₂,V₂O₅), particles of transition metal sulfides (e.g., MoS₂, TiS₂), andparticles of conductive polymers (e.g., polyaniline, polypyrrole,polythiophene, polyacetylene, poly-p-phenylene, polyvinylcarbazole).

In the electrode of the present invention, the active material particles(B) preferably include coated active material particles whose surface isat least partially coated with a coating agent containing a coatingresin and a conductive additive.

In the embodiment illustrated in FIG. 2, positive electrode activematerial particles 14 are coated with a coating agent 15. The coatingagent contains a coating resin. If the positive electrode activematerial particles are coated with a coating agent, change in the volumeof the electrode can be reduced, and the expansion of the electrode canbe suppressed. Examples of the coating resin include vinyl resins,urethane resins, polyester resins, polyamide resins, epoxy resins,polyimide resins, silicone resins, phenol resins, melamine resins, urearesins, aniline resins, ionomer resins, and polycarbonates. Among theseresins, vinyl resins, urethane resins, polyester resins, and polyamideresins are preferred.

The conductive paths formed of the conductive fibers 13 are in contactwith the positive electrode active material particles 14 around theconductive paths. Such contact of the conductive paths with the positiveelectrode active material particles allows the electrons generated fromthe positive electrode active material particles to quickly reach theconductive paths and flow through the conductive paths to the currentcollector. Since the conductive paths are formed of the conductivemember that is an electronically conductive material, electrons cansmoothly reach the current collector.

In the case where the active material particles are coated activematerial particles, a conductive path in contact with the coating agentcan be regarded as being in contact with the active material particles.

In an electrode without such a conductive path, electrons have to passthrough active material particles, which are not highly electronicallyconductive, and thus they are less likely to smoothly reach the currentcollector. In the case where electrons are conducted via a conductiveadditive consisting of particulates, there is electrical resistancebetween the particles. In addition, since the particles of theconductive additive are not continuously joined to one another,electrons unavoidably pass through regions with high electricalresistance. Electrons are thus less likely to smoothly reach the currentcollector.

In the foregoing description, the move of electrons is describedreferring to cases in which electrons generated from the positiveelectrode active material particles flow to the current collector.Similarly, electrons flowing from the current collector to the positiveelectrode active material particles can pass through conductive pathsand smoothly reach the positive electrode active material particles.That is, the same effects can be obtained in charging and discharging.

The positive electrode 10 may further contain a conductive additive 16.

The conductive additive is selected from conductive materials.

Specific examples thereof include, but not limited to, metals [e.g.,aluminum, stainless steel (SUS), silver, gold, copper, titanium], carbon[e.g., graphite, carbon blacks (acetylene black, ketjen black, furnaceblack, channel black, thermal lamp black)], and mixtures thereof.

These conductive additives may be used alone or two or more thereof maybe used in combination. Alloys or metal oxides thereof may be used. Fromthe viewpoint of the electrical stability, aluminum, stainless steel,carbon, silver, gold, copper, titanium, and mixtures thereof arepreferred, silver, gold, aluminum, stainless steel, and carbon are morepreferred, and carbon is still more preferred. The conductive additivemay be a particulate ceramic material or resin material coated with aconductive material (any of the metals mentioned above as materials ofthe conductive additive) by plating, for example.

The conductive additive 16 may be contained in the coating agent 15, ormay be in contact with the positive electrode active material particles14. If the conductive additive is contained in the coating agent or incontact with the positive electrode active material particles, electronconductivity from the positive electrode active material particles tothe conductive paths can be further enhanced.

If the electrode for lithium ion batteries of the present invention is anegative electrode, the electrode may have the same configuration exceptthat negative electrode active material particles are used as activematerial particles (B) instead of the positive electrode active materialparticles.

Examples of the negative electrode active material particles includeparticles of graphite, non-graphitizable carbon, amorphous carbon,products obtained by firing polymer compounds (e.g., products obtainedby firing and carbonizing phenolic resins or furan reins), cokes (e.g.,pitch coke, needle coke, petroleum coke), carbon fibers, conductivepolymers (e.g., polyacetylene, polypyrrole), tin, silicon, and metalalloys (e.g., lithium-tin alloy, lithium-silicon alloy, lithium-aluminumalloy, lithium-aluminum-manganese alloy), and complex oxides of lithiumand transition metals (e.g., Li₄Ti₅O₁₂).

Also in the negative electrode, the conductive path is in contact withnegative electrode active material particles around the conductive path.As in the case of the positive electrode, electrons generated from thenegative electrode active material particles quickly reach theconductive path and pass through the conductive path smoothly to thecurrent collector. Similarly, electrons flowing from the currentcollector to the negative electrode active material particles cansmoothly reach the negative electrode active material.

FIG. 3 is a schematic cross-sectional view of an example of anotherembodiment of the electrode for lithium ion batteries of the presentinvention.

In an electrode (positive electrode) 110 according to the embodimentillustrated in FIG. 3, the conductive member (A) includes conductivefibers 113 constituting a woven fabric. The woven fabric is composed ofwarp yarns 113 a and weft yarns 113 b formed of the conductive fibers.The electrode (positive electrode) 110 according to the embodimentillustrated in FIG. 3 has the same configuration as that according tothe embodiment illustrated in FIG. 2, except that a fabric-form fiberstructure corresponding to the nonwoven fabric in FIG. 2 is a wovenfabric.

The woven fabric may be woven by any method. Usable woven fabricsinclude those woven by plain weaving, twill weaving, satin weaving, orpile weaving.

Instead of the woven fabric, a knitted fabric composed of the conductivefibers may be used.

The knitted fabric may be knitted by any method. Usable knitted fabricsinclude those knitted by weft knitting, warp knitting, or circularknitting.

Similar to the nonwoven fabric, the woven fabric and the knitted fabrichave many voids between the conductive fibers constituting them. Anelectrode for lithium ion batteries can be formed by filling the voidswith active material particles.

At least part of the conductive fibers 113 has a portion extending tothe first main surface 111 and another portion extending to the secondmain surface 112. In other words, at least part of the conductive fibers113 forms a conductive path that electrically connects the first mainsurface 111 and the second main surface 112.

Other factors such as preferred conductive fibers and preferred activematerials are the same as those for the electrode for lithium ionbatteries illustrated in FIG. 2. The description thereof is omittedhere.

The electrode 110 can serve as a negative electrode for lithium ionbatteries according to the present invention if the active materialparticles (B) are negative electrode active material particles.

FIG. 4 is a schematic cross-sectional view of an example of yet anotherembodiment of the electrode for lithium ion batteries of the presentinvention.

In an electrode (positive electrode) 210 according to the embodimentillustrated in FIG. 4, the conductive member (A) includes conductivefibers 213 dispersed between a first main surface 211 and a second mainsurface 212.

The conductive fibers 213 are not part of a structure formed ofconductive fibers, such as the nonwoven fabric, the woven fabric, or theknitted fabric illustrated in FIG. 2 and FIG. 3. This electrode isproduced using a slurry containing the conductive fibers and the activematerial particles. The method for producing the electrode according tothe embodiment illustrated in FIG. 4 will be described later. In thiselectrode, the conductive fibers are dispersed in the active materialparticles. This electrode should not be regarded as one in which voidsbetween fibers are filled with active material particles.

At least part of the conductive fibers 213 has a portion extending tothe first main surface 211 and another portion extending to the secondmain surface 212. In other words, at least part of the conductive fibers213 forms a conductive path that electrically connects the first mainsurface 211 to the second main surface 212.

In FIG. 4, a conductive fiber 213 a shows an example of a singleconductive fiber forming a conductive path. Two conductive fibers 213 bshow an example of two fibers in contact with each other forming aconductive path.

Other factors such as preferred conductive fibers and preferred activematerials are the same as those for the electrode for lithium ionbatteries illustrated in FIG. 2. The description thereof is omittedhere. The electrode 210 can serve as a negative electrode for lithiumion batteries according to the present invention if the active materialparticles (B) are negative electrode active material particles.

In the electrode for lithium ion batteries according to the embodimentillustrated in FIG. 4, the conductive fibers as the conductive member(A) and the active material particles (B) may be fixed onto a film (E)such that the fixed shape can be retained loosely to the extent thatthey do not flow. If the film (E) is made of a material having highconductivity (conductive material), the film (E) can substitute for acurrent collector. In addition, the conductivity is not inhibited evenif the film (E) contacts with a current collector. Thus, the film ispreferably made of a conductive material. The film (E) is not shown inFIG. 4. The method of producing the electrode for lithium ion batteriesin which the conductive fibers as the conductive member (A) and theactive material particles (B) are fixed onto the film (E) will bedescribed later.

In the electrode for lithium ion batteries of the present invention, theconductive fibers as the conductive member (A) and the active materialparticles (B) may be fixed by a resin (F) to keep the conductive fibersdispersed in the active material particles in a lithium ion battery.

FIG. 5 is a schematic cross-sectional view of an example of yet anotherembodiment of the electrode for lithium ion batteries of the presentinvention. An electrode (positive electrode) 210′ illustrated in FIG. 5has the same configuration as that according to the embodimentillustrated in FIG. 4 except that the conductive fibers 213 as theconductive member (A) and the positive electrode active materialparticles 14 as the active material particles (B) are fixed by a resin214.

Examples of the resin (F) include vinyl resins, urethane resins,polyester resins, and polyamide resins.

The method for producing the electrode for lithium ion batteries inwhich the conductive fibers as the conductive member (A) and the activematerial particles (B) are fixed by a resin (F) will be described later.

FIG. 6 is a schematic cross-sectional view of an example of yet anotherembodiment of the electrode for lithium ion batteries of the presentinvention.

In an electrode (positive electrode) 310 according to the embodimentillustrated in FIG. 6, the conductive member (A) includes a resin 313provided with conductivity and constituting a part of a foamed resin.The foamed resin has many voids. An electrode for lithium ion batteriescan be formed by filling the voids with the active material particles.

The resin provided with conductivity may be, for example, a resinprovided with conductivity obtained by forming a conductive thin film onthe surface of a resin, or a resin provided with conductivity obtainedby mixing a resin with a conductive filler such as a metal or carbonfibers. The resin itself may be a conductive polymer. The conductivepolymer may be further provided with conductivity.

The conductive thin film may be formed on the surface of a resin by, forexample, metal plating, a deposition treatment, or a sputteringtreatment.

In the embodiment illustrated in FIG. 6, a resin 313 provided withconductivity is continuous from a first main surface 311 to a secondmain surface 312. The resin 313 provided with conductivity forms aconductive path that electrically connects the first main surface 311 tothe second main surface 312.

The foamed resin including the resin provided with conductivity ispreferably a resin foam, such as a polyurethane foam, a polystyrenefoam, a polyethylene foam, or a polypropylene foam.

In particular, the foamed resin is preferably a polyurethane foam whosesurface is plated with a metal such as nickel.

In the electrode of the present invention, if the conductive member (A)is a foamed resin including a resin provided with conductivity, thefoamed resin including a resin provided with conductivity preferably hasan electrical conductivity of 100 mS/cm or more, more preferably 150 to500 mS/cm.

The electrical conductivity of the foamed resin can be determined by thefour-terminal method. If the foamed resin including a resin providedwith conductivity has an electrical conductivity of 100 mS/cm or more,the conductive paths that are formed of the conductive fibers andconnect the first main surface to the second main surface have smallelectrical resistance. This advantageously enables smooth transfer ofelectrons from the active material far from the current collector.

Preferred active material particles are the same as those for theelectrode for lithium ion battery illustrated in FIG. 2. The descriptionthereof is omitted here. If the active material particles (B) arenegative electrode active material particles, the electrode 310 canserve as a negative electrode for lithium ion batteries according to thepresent invention.

In the electrode for lithium ion batteries of the present invention,including the embodiments illustrated in FIGS. 2 to 6, the proportion byvolume of the conductive member (A) is preferably 0.1 to 15 vol %, morepreferably 1 to 6 vol %, based on the volume of the electrode. In otherwords, the volume of the conductive member (A) in the electrode ispreferably relatively small. A small volume of the conductive member (A)indicates that voids not occupied by the conductive member (A) can befilled with a large number of active material particles (B). By fillingthe voids with a large number of active material particles (B), anelectrode for lithium ion batteries with high capacity can be obtained.

As used herein, the term “a large number of active material particles”does not mean specification of the number of active materials present inthe electrode, but means that a sufficient number of active materialparticles to fill the voids between the first main surface and thesecond main surface are present.

In the electrode for lithium ion batteries of the present invention, theproportion by volume of the active material particles (B) is preferably30 to 80 vol %, more preferably 45 to 60 vol %, based on the volume ofthe electrode. If the proportion of the active material particles (B) islarge, the electrode for lithium ion batteries can have high capacity.

In the electrode for lithium ion batteries of the present invention, theratio (V_(A)/V_(B)) of the volume V_(A) of the conductive member (A) tothe volume V_(B) of the active material particles (B) is preferably0.00125 to 0.5, more preferably 0.03 to 0.35.

If the volume of the conductive member (A) is small and that of theactive material particles (B) is large, the electrode for lithium ionbatteries can have high capacity.

The volume of the conductive member (A) and that of the active materialparticles (B) are determined by the following method.

An electrode containing a mixture of the conductive member (A) and theactive material particles (B) is prepared by drying an electrolytesolution and the like. The weight [w (g)] per cm² of the electrode andthe film thickness [t (cm)] of the electrode are measured. The volumesof the conductive member (A) and the active material particles (B) arecalculated based on the weight, the thickness, the true specific gravity[dA (g/cm³)] of the conductive member (A), the true specific gravity [dB(g/cm³)] of the active material particles (B), and the proportions (WAand WB) of the conductive member (A) and the active material particles(B) added based on the total weight of the components constituting theelectrode of the present invention.

V _(A)=(w×WA/dA)/(t×1)×100

V _(B)=(w×WB/dB)/(t×1)×100

The method of producing the electrode for lithium ion batteries of thepresent invention will be described below.

One aspect of the present invention provides a method of producing theelectrode for lithium ion batteries of the providing a structure (Z)that contains the conductive member (A), has voids therein, and has afirst main surface and a second main surface; step (P2) of applying aslurry (X) containing the active material particles (B) to the firstmain surface or the second main surface of the structure (Z); and step(P3) of filling the voids in the structure (Z) with the active materialparticles (B) by pressurization or depressurization.

The production method according to this aspect is suitable for producingthe electrodes for lithium ion battery according to the embodimentsillustrated in FIG. 2, FIG. 3, and FIG. 6.

First, a structure (Z) is provided (step P1). The structure (Z) includesthe conductive member (A), has voids therein, and has a first mainsurface and a second main surface.

The structure (Z) has a large number of voids. The term “void” as usedherein refers to space that has an opening and is surrounded by thematerials constituting the structure (conductive fibers or resinprovided with conductivity). The voids have no clear boundariestherebetween, and are joined to each other. Accordingly, the term “alarge number of voids” does not mean counting the number of voids in thestructure (Z) to specify the number of voids, but means that voids forbeing filled with active material particles occupy a large volume in thestructure (Z) and that the structure (Z) has space that can be filledwith a large number of active material particles.

The structure (Z) is preferably a nonwoven fabric including theconductive member (A) made of conductive fibers, a woven fabric orknitted fabric including the conductive member (A) made of conductivefibers, or a foamed resin including the conductive member (A) made of aresin provided with conductivity. The descriptions of the nonwovenfabric, woven fabric, knitted fabric, and foamed resin are the same asthose for the electrode for lithium ion batteries of the presentinvention, and thus are omitted here.

FIG. 7(a) and FIG. 7(b) illustrates a step of filling voids in astructure with active material particles. These figures illustrate anembodiment where the structure is a nonwoven fabric.

Next, a slurry (X) containing the active material particles (B) isapplied to the first main surface or the second main surface of thestructure (Z) (step P2).

The active material particles (B) may be any of those mentioned in thedescription of the electrode for lithium ion batteries of the presentinvention. The active material particles (B) are preferably coatedactive material particles. The coated active material particles can beobtained as follows, for example. Particles of a lithium ion batteryactive material are fed into a universal mixer. While stirring at 30 to500 rpm, a resin solution containing a resin for coating the lithium ionbattery active material is added dropwise over 1 to 90 minutes, andfurther a conductive additive is added. While stirring continues, thetemperature is raised to 50° C. to 200° C. After the pressure decreasesto 0.007 to 0.04 MPa, the mixture is held for 10 to 150 minutes, wherebycoated active material particles are obtained.

The slurry containing the active material particles (B) is preferably asolvent slurry (X1) containing a solvent (C) or an electrolyte solutionslurry (X2) containing an electrolyte solution (D).

Examples of the solvent (C) include water, 1-methyl-2-pyrolidone(N-methylpyrolidone), methyl ethyl ketone, dimethylformamide,dimethylacetamide, N,N-dimethylaminopropylamine, and tetrahydrofuran.

The electrolyte solution (D) may be an electrolyte solution containingan electrolyte and a nonaqueous solvent and usable for producing lithiumion batteries.

An electrolyte that is used for usual electrolyte solutions may be used.Examples thereof include lithium salts of inorganic acids such as LiPF₆,LiBF₄, LiSbF₆, LiAsF₆, and LiClO₄ and lithium salts of organic acidssuch as LiN(CF₃SO₂)₂, LiN(C₂F₅SO₂)₂, and LiC(CF₃SO₂)₃. From theviewpoint of the output power of the battery and the charge-dischargecycle characteristics, LiPF₆ is preferred.

A nonaqueous solvent that is used for usual electrolyte solutions may beused. Examples thereof include lactone compounds, cyclic or acycliccarbonates, acyclic carboxylic acid esters, cyclic or acyclic ethers,phosphoric acid esters, nitrile compounds, amide compounds, sulfone,sulfolane, and mixtures thereof.

The nonaqueous solvents may be used alone or in combination of two ormore.

Among the nonaqueous solvents, lactone compounds, cyclic carbonates,acyclic carbonates, and phosphates are preferred from the viewpoint ofthe output power of the battery and the charge-discharge cyclecharacteristics. Lactone compounds, cyclic carbonates, and acycliccarbonates are more preferred. Mixtures of cyclic carbonates and acycliccarbonates are still more preferred. A mixture of ethylene carbonate(EC) and diethyl carbonate (DEC) is particularly preferred.

The slurry (X) is preferably prepared by dispersing and slurrying theactive material particles (B) and optionally a conductive additive and abinder at a concentration of 10 to 60% by weight based on the weight ofthe solvent or the electrolyte solution.

The conductive additive may be any of those mentioned in the descriptionof the electrode for lithium ion batteries of the present invention.

Examples of the binder include polymer compounds such as starch,polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose,polyvinylpyrolidone, tetrafluoroethylene, styrene-butadiene rubber,polyethylene, and polypropylene.

The slurry containing the active material particles (B) can be appliedto the first main surface or the second main surface of the structure(Z) with any application device. Examples thereof include a bar coaterand a brush.

FIG. 7(a) schematically illustrates a slurry applied to a second mainsurface of a nonwoven fabric as a structure. A slurry containingpositive electrode active material particles 14 is applied to a secondmain surface 62 of a nonwoven fabric 60.

Then, the voids in the structure (Z) are filled with the active materialparticles (B) by pressurization or depressurization (step P3).

The pressurization may be performed by pressing from above the surfacewith the slurry using a pressing machine. The depressurization may beperformed by suction using a vacuum pump with filter paper or meshapplied to the surface of the structure to which the slurry is notapplied.

The structure (Z) has voids. By the pressurization or depressurization,the voids in the structure (X) can be filled with the active materialparticles (B).

FIG. 7(a) shows an arrow indicating the direction of pressurization fromabove a surface with a slurry and an arrow indicating the direction ofdepressurization from below filter paper 70. FIG. 7(b) illustrates anelectrode 10 for lithium ion batteries in which voids in the structure(Z) are filled with the active material particles (B). The electrode forlithium ion batteries illustrated in FIG. 7(b) is the same as theelectrode 10 for lithium ion batteries illustrated in FIG. 2.

If the slurry containing the active material particles (B) is a solventslurry (X1) containing a solvent (C), step (P4 ) of removing the solvent(C) is further preferably performed after step (P3).

If the slurry containing the active material particles (B) is anelectrolyte solution slurry (X2) containing an electrolyte solution (D),the voids in the structure (Z) are filled with the active materialparticles (B) and the electrolyte solution (D). Such a configuration ispreferable as an electrode for lithium ion batteries.

The use of the electrolyte solution slurry is preferred because unlikethe use of the solvent slurry, it does not cause mixing of impuritiesother than the electrolyte solution into the liquid component in theelectrode for lithium ion batteries.

Also in the case where the structure (Z) is not a nonwoven fabric but awoven fabric or knitted fabric containing the conductive member (A) or afoamed resin including a resin provided with conductivity, an electrodefor lithium ion batteries can be produced by filling the active materialparticles into the voids in the structure by the above step.

Another aspect of the present invention provides a method of producingthe electrode for lithium ion batteries of the present invention, themethod including: step (Q1) of applying a slurry (Y) containing theconductive member (A) and the active material particles (B) to a film(E); and

step (Q2) of fixing the active material particles (B) and the conductivemember (A) onto the film (E) by pressurization or depressurization.

The method according to this aspect is suitable for producing theelectrode for lithium ion batteries according to the embodimentillustrated in FIG. 4. In particular, this method is suitable forproducing a positive electrode for lithium ion batteries.

FIG. 8(a) and FIG. 8(b) schematically illustrates a step of fixingactive material particles and a conductive member onto a film.

First, the slurry (Y) containing the conductive member (A) and theactive material particles (B) is applied to a film (E) (step Q1).

The slurry (Y) may be, for example, a slurry obtained by furtherdispersing conductive fibers as the conductive member (A) into theslurry (X) described above.

The conductive fibers may be any of the conductive fibers described forthe electrode for lithium ion batteries of the present invention. Theconductive fibers are preferably independent from one another. Theypreferably do not have a three-dimensional structure such as a nonwovenfabric, a woven fabric, or a knitted fabric. If the conductive fibersare independent from one another, the fibers are dispersed in theslurry.

The slurry (Y) is preferably an electrolyte solution slurry (Y1)containing an electrolyte solution (D). The electrolyte solution (D) maybe the same as the electrolyte solution (D) for the electrolyte solutionslurry (X2) described above. The slurry (Y) may be a solvent slurrycontaining a solvent (C).

The film (E) is preferably a film capable of separating the activematerial particles and the conductive member from the electrolytesolution and the solvent in the subsequent pressurization ordepressurization step. If the film (E) is made of a material having highconductivity (conductive material), the film (E) can substitute for thecurrent collector. In addition, the conductivity is not inhibited evenif the film (E) contacts with the current collector. Thus, the film ispreferably made of a conductive material. For example, the film (E) issuitably made of a material with an electrical conductivity of 100 mS/cmor more.

Examples of materials with such properties include filter papercontaining conductive fibers such as carbon fibers and metal mesh.

The metal mesh is preferably made of stainless steel. Examples of such ametal mesh include SUS316-made twilled dutch weave wire mesh (availablefrom Sunnet Industrial Co., Ltd.). The metal mesh preferably has anopening size that does not allow the active material particles or theconductive member to pass through the mesh. For example, a metal mesh of2300 mesh is preferably used.

The slurry (Y) can be applied to the film (E) with any applicationdevice. Examples thereof include a bar coater and a brush.

FIG. 8(a) schematically illustrates a slurry applied to a film. A slurrycontaining active material particles 14 and conductive fibers 213 isapplied to a filter paper 470 as a film.

Next, the active material particles (B) and the conductive member (A)are fixed onto the film (E) by pressurization or depressurization (stepQ2).

The pressurization or the depressurization can be performed in the samemanner as in step (P3). By the pressurization or depressurization, theelectrolyte solution or the solvent is removed from the slurry (Y), andthe conductive fibers as the conductive member (A) and the activematerial particles (B) are fixed onto the film (E) such that the fixedshape is retained loosely to the extent that they do not flow.

FIG. 8(b) illustrates an electrode 210 in which the conductive fibers213 as the conductive member (A) and the active material particles 14are fixed on the filter paper 470.

If the film (E) in the electrode 210 is made of a conductive material,the film (E) can substitute for a current collector. Alternatively, thefilm (E) and a current collector may be brought into contact so thatthey can serve as one current collector. Accordingly, a second mainsurface 212 in the electrode 210 can be defined as a portion where theconductive fibers 213 as the conductive member (A) contact with thefilter paper 470.

If the film (E) is made of a non-conductive material, the film (E) ispreferably disposed on the separator side. Alternatively, the film (E)may be used as a separator. Examples of the film made of anon-conductive material include an aramid separator (available fromJapan Vilene Company, Ltd.).

If the slurry (Y) is an electrolyte solution slurry (Y1) containing anelectrolyte solution (D), the film (E) is preferably a film impermeableto the active material particles (B) but permeable to the electrolytesolution (D), and the electrolyte solution (D) is preferably allowed topermeate the film (E) by pressurization or depressurization so as to beremoved in step (Q2).

A press step (Q3) of pressurizing the slurry (Y) at a higher pressure ispreferably performed after step (Q2).

In the press step (Q3), the pressure difference is greater than that inthe pressurization or depressurization in step (Q2) in order to improvethe density of the active material particles (B). The “press step (Q3)”encompasses both pressurization in the case where depressurization isperformed in step (Q2) and pressurization at a higher pressure in thecase where pressurization is performed in step (Q2).

It is preferred to further perform step (Q4) of transferring theelectrode for lithium ion batteries fixed onto the film (E) to a mainsurface of a current collector or a separator so as to produce anelectrode for lithium ion batteries having a first main surface thereofon the main surface of the separator or produce an electrode for lithiumion batteries having a second main surface thereof on the main surfaceon the current collector.

If step (Q4) is performed, the electrode for lithium ion batteries fixedonto the film (E) is preferably transferred by bringing a main surface[first main surface 211 in FIG. 8(b)] of the electrode opposite the film(E) into contact with a main surface of a current collector or aseparator.

If the film (E) is made of a conductive material and substitutes for acurrent collector, the electrode is preferably transferred by bringing amain surface opposite the film (E) into contact with a main surface of aseparator. If the film (E) does not substitute for a current collector,a step of removing the film (E) is preferably performed after step (Q4).

Yet another aspect of the present invention provides a method ofproducing the electrode for lithium ion batteries of the presentinvention, the method including: step (T1) of applying a slurry (Y)containing the conductive member (A) and the active material particles(B) to a current collector to form a slurry layer on the currentcollector; and

step (T2) of disposing a separator on the slurry layer and absorbingliquid from an upper surface of the separator so as to fix the activematerial particles (B) and the conductive member (A) between the currentcollector and the separator.

The method according to this aspect is suitable for producing theelectrode for lithium ion batteries according to the embodimentdescribed with reference to FIG. 4, where the conductive member includesconductive fibers dispersed between the first main surface and thesecond main surface. In particular, the method is suitable for producinga negative electrode for lithium ion batteries.

FIG. 9(a), FIG. 9(b) and FIG. 9(c) schematically illustrates a step offixing active material particles and a conductive member between acurrent collector and a separator.

First, a slurry (Y) containing the conductive member (A) and the activematerial particles (B) is applied to a current collector so as to form aslurry layer (step Tl).

The current collector may be, for example, copper, aluminum, titanium,stainless steel, nickel, baked carbon, conductive polymer, or conductiveglass.

The slurry (Y) may be the same as the slurry (Y) described above withreference to FIG. 8. Examples thereof include a slurry obtained byfurther dispersing conductive fibers as the conductive member (A) intothe slurry (X).

The slurry (Y) is preferably an electrolyte solution slurry (Y1)containing an electrolyte solution (D). The electrolyte solution (D) maybe the same as the electrolyte solution (D) described above for theelectrolyte solution slurry (X2). The slurry (Y) may be a solvent slurrycontaining a solvent (C).

The slurry (Y) can be applied to the current collector with anyapplication device. Examples thereof include a bar coater and a brush.

FIG. 9(a) schematically illustrates a slurry layer 225 formed byapplying a slurry to a current collector 50. A slurry containingnegative electrode active material particles 24 and conductive fibers223 is applied to the current collector 50. The applied slurry forms theslurry layer 225.

In the embodiment illustrated in FIG. 9(a), the negative electrodeactive material particles 24 are coated with a coating agent 25. Theslurry contains a conductive additive 26.

The conductive fibers 223, the coating agent 25, and the conductiveadditive 26 are the same as the conductive fibers 213, the coating agent15, and the conductive additive 16 described above for the electrode(positive electrode) for lithium ion batteries of the present invention.

Also, the negative electrode active material particles 24 are the sameas the negative electrode active material particles described for theelectrode for lithium ion batteries of the present invention.

Next, a separator is disposed on the slurry layer, and liquid isabsorbed from the upper surface of the separator so as to fix the activematerial particles (B) and the conductive member (A) between the currentcollector and the separator (step T2). As illustrated in FIG. 9(b), aseparator 30 is disposed on a slurry layer 225, and then liquid isabsorbed from the upper surface of the separator 30.

Examples of the separator include aramid separators (available fromJapan Vilene Company, Ltd.), microporous polyethylene films, microporouspolypropylene films, multilayer films composed of a porous polyethylenefilm and a porous polypropylene film, nonwoven fabrics containingpolyester fibers, aramid fibers, or glass fibers, and separatorscontaining ceramic microparticles such as silica, alumina, or titaniaparticles attached to the surface of any of these films or nonwovenfabrics.

The liquid absorption may be performed as follows: Pressurization fromthe upper surface or the lower surface of the separator is performed toallow liquid to exude from the upper surface of the separator, and theexuded liquid is absorbed. Or, the liquid absorption may be performed bydepressurization from the upper surface of the separator to suctionliquid. Alternatively, the liquid absorption may be performed from theupper surface of the separator by disposing a liquid-absorbing materialon the upper surface of the separator.

The liquid-absorbing material may be liquid-absorbing cloth such astowel, paper, or a liquid-absorbing resin.

By absorption of liquid, the electrolyte solution or the solvent isremoved from the slurry (Y). The conductive fibers as the conductivemember (A) and the active material particles (B) are thus fixed betweenthe current collector and the separator so that the fixed shape isretained loosely to the extent that they do not flow.

The pressurization may be performed by any method. Various methods maybe employed. Examples thereof include pressurization with a knownpressing machine and pressurization by disposing a heavy material as aweight. During pressurization, vibrations may be applied with anultrasonic vibrator or the like. The pressure in the pressurization fromthe upper surface or the lower surface of the separator is preferably0.8 to 41 kg/cm², more preferably 0.9 to 10 kg/cm². If the pressure iswithin this range, the conductive paths inside the electrode can befavorably formed, which advantageously increases the capacity of abattery.

FIG. 9(c) illustrates an electrode 220 in which conductive fibers 223 asthe conductive member (A) and the active material particles 24 are fixedbetween a current collector 50 and a separator 30.

In the electrode 220, a first main surface 221 of the electrode is incontact with a separator 30. A second main surface 222 of the electrodeis in contact with a current collector 50.

Such a method of producing an electrode for lithium ion batteriesproduces an electrode sandwiched between a separator and a currentcollector. Such a method is preferred because it eliminates the need foran additional step of disposing a separator and a current collector onboth sides of the electrode, and enables the production of an electrodewith a structure preferred for a bipolar electrode in fewer steps.

Another aspect of the present invention provides a method of producingan electrode for lithium ion batteries, the electrode including: a firstmain surface to be located adjacent to a separator of a lithium ionbattery; and a second main surface to be located adjacent to a currentcollector of the lithium ion battery, wherein the electrode contains,between the first main surface and the second main surface, a conductivemember (A) made of an electronically conductive material, a large numberof active material particles (B), and a resin (F), at least part of theconductive member (A) forms a conductive path that electrically connectsthe first main surface to the second main surface, and the conductivepath is in contact with the active material particles (B) around theconductive path,

the method including step (R1) of hot-pressing a composition for anelectrode containing the conductive member (A), the active materialparticles (B), and the resin (F) so as to fix the conductive member (A)and the active material particles (B) by the resin (F).

The method according to the above aspect is suitable for producing theelectrode for lithium ion batteries according to the embodimentdescribed with reference to FIG. 5.

FIG. 10(a) and FIG. 10(b) schematically illustrates a step of fixingactive material particles and a conductive member by a resin.

First, a composition for an electrode is prepared which contains aconductive member (A), active material particles (B), and a resin (F).

The conductive member (A) preferably includes conductive fibers that areindependent from one another, as in the case of the conductive member(A) preferred for the method of producing the electrode for lithium ionbatteries according to the aspect described with reference to FIG. 8(a)and FIG. 8(b)

Preferred examples of the resin (F) include vinyl resins, urethaneresins, polyester resins, and polyamide resins. These resins arepreferred from the viewpoint of moldability.

In the composition for an electrode, the resin (F) may be in the form ofa resin solution in a solvent or in the form of solid, such as a pelletthat is fluidized when heated.

If the active material particles (B) are coated active materialparticles, the coating resin contained in the coating agent may be theresin (F).

If the resin (F) in the composition for an electrode is in the form of aresin solution in a solvent, the conductive member (A) and the activematerial particles (B) are preferably dispersed in the resin solution.Also in the case where the resin (F) is in the form of solid, the resin(F), the conductive member (A), and the active material particles (B)are preferably dispersed, not localized in a particular portion.

The composition for an electrode thus prepared is hot-pressed so thatthe conductive member (A) and the active material particles (B) arefixed by the resin (F) (step R1).

The composition may be hot-pressed by any method. For example, thecomposition may be hot-pressed by a method in which, as illustrated inFIG. 10(a), a composition for an electrode containing positive electrodeactive material particles 14, conductive fibers 213, a resin 214 isapplied to a plate 570 such as a metal plate and then hot-pressed fromthe upper surface.

The composition for an electrode may be applied by any applicationdevice. Examples thereof include a bar coater or a brush. Thehot-pressing may be performed using a usual hot-pressing device.

In the case where the resin (F) is the coating resin of the coatedactive material particles, when the conductive member (A) and the coatedactive material particles are applied to a plate and hot-pressed, theconductive member and the (coated) active material particles are fixedby coating resin melted by heat.

The active material particles fixed by the coating resin may be coatedactive material particles that remains coated with the coating resin ormay be active material particles from which the coating has peeled off.

The conditions for the hot-pressing may be determined according to thecuring conditions of the resin to be used and are not limited. Forurethane resin, for example, the hot-pressing is preferably performed at100° C. to 200° C. and 0.01 to 5 MPa for 5 to 300 seconds.

For vinyl resin, the hot-pressing may be performed at 80° C. to 180° C.and 0.01 to 5 MPa for 5 to 300 seconds.

By hot-pressing, as illustrated in FIG. 10(b), an electrode 210′ inwhich conductive fibers 213 and positive electrode active materialparticles 14 are fixed by a resin 214 can be produced.

A lithium ion battery including the electrode for lithium ion batteriesof the present invention can be obtained by assembling the electrode ofthe present invention with a counter electrode, placing the assembly,together with a separator, into a cell case, pouring an electrolytesolution to the case, and sealing the case.

Alternatively, such a lithium ion battery can be obtained by forming apositive electrode on one surface of a current collector and a negativeelectrode on the other surface to produce a bipolar electrode, stackingthe bipolar electrode on a separator, placing the stack into a cellcase, pouring an electrolyte solution, and sealing the cell case.

In the lithium ion battery, either one of the positive electrode and thenegative electrode may be the electrode for lithium ion batteries of thepresent invention, or both of the positive electrode and the negativeelectrode may be the electrode for lithium ion batteries of the presentinvention.

Examples of the separator include microporous polyethylene films,microporous polypropylene films, multi-layer films composed of a porouspolyethylene film and a porous polypropylene film, nonwoven fabrics madeof polyester fibers, aramid fibers, or glass fibers, and separatorscontaining ceramic microparticles such as silica, alumina, or titaniaparticles attached to the surface of any of these films or nonwovenfabrics.

The electrolyte solution may be the electrolyte solution described aboveas the electrolyte solution (D).

EXAMPLES

The present invention will be specifically described below based onexamples. The present invention is not limited to the examples, as longas it does not departs from the scope of the present invention. The“part(s)” refers to part(s) by weight and “%” refers to % by weight, ifnot otherwise specified.

<Preparation of Coating Resin Solution>

A four-necked flask equipped with a stirring device, a thermometer, areflux condenser, a dropping funnel, and a nitrogen gas injection tubewas charged with 83 parts of ethyl acetate and 17 parts of methanol. Thetemperature was then raised to 68° C. Subsequently, a monomer mixturecontaining 242.8 parts of methacrylic acid, 97.1 parts of methylmethacrylate, 242.8 parts of 2-ethylhexyl methacrylate, 52.1 parts ofethyl acetate, and 10.7 parts of methanol and an initiator solutioncontaining 0.263 parts of 2,2′-azobis(2,4-dimethylvaleronitrile)dissolved in 34.2 parts of ethyl acetate were added dropwise through thedropping funnel continuously over four hours under stirring, whileblowing nitrogen into the four-necked flask. Thus, radicalpolymerization was performed. After the completion of the dropwiseaddition, an initiator solution containing 0.583 parts of2,2′-azobis(2,4-dimethylvaleronitrile) in 26 parts of ethyl acetate wascontinuously added over two hours through the dropping funnel. Thepolymerization was further continued at the boiling point for fourhours. The solvent was removed and 582 parts of a resin was obtained.Thereafter, 1,360 parts of isopropanol was added to the resin, so that acoating resin solution containing a vinyl resin was obtained. Thecoating resin solution had a resin concentration of 30° by weight.

<Pulverization of Positive Electrode Active Material Particles>

An amount of 100 parts by weight of LiCoO₂ powder [available from NipponChemical Industrial Co., Ltd., CELLSEED C-5H], 100 parts by weight ofwater, and 1200 parts by weight of alumina balls (Φ 3 mm) were put in apot mill and the powder was pulverized for 20 minutes. Thus, 100 partsby weight of LiCoO₂ powder with an average particle size of 2.3 μm wasobtained.

<Pulverization of Negative Electrode Active Material Particles>

An amount of 100 parts by weight of non-graphitizable carbon [availablefrom Kureha Battery Materials Japan Co., Ltd., CARBOTRON (registeredtrademark) PS(F)], 200 parts by weight of water, and 1000 parts byweight of zirconia balls (Φ 0.1 mm) were put in a pot mill and thecarbon was pulverized for 15 minutes. Thus, 100 parts by weight ofnon-graphitizable carbon with an average particle size of 2.5 μm wasobtained.

<Preparation of Coated Positive Electrode Active Material Particles(B-1)>

An amount of 96 parts by weight of LiCoO₂ powder [available from NipponChemical Industrial Co., Ltd., CELLSEED C-8G] was put into a universalmixer. While stirring at 150 rpm at room temperature, the coating resinsolution (resin solid concentration: 30% by weight) was added dropwiseover 60 minutes such that the amount of the resin solid added was 2parts by weight. The resulting mixture was further stirred for 30minutes.

Subsequently, while stirring, 2 parts by weight of acetylene black[available from Denka Company Limited., DENKA BLACK (registeredtrademark)] was added to the mixture in three steps. The temperature wasraised to 70° C. while stirring for 30 minutes. The pressure was reducedto 100 mmHg and the mixture was held for 30 minutes. In this manner,coated positive electrode active material particles (B-1) were obtained.

<Preparation of Coated Positive Electrode Active Material Particles(B-2)>

Coated positive electrode active material particles (B-2) were obtainedin the same manner as in the preparation of (B-1) except that the 96parts by weight of LiCoO₂ powder [available from Nippon ChemicalIndustrial Co., Ltd., CELLSEED C-8G] was changed to the LiCoO₂ powderwith an average particle size of 2.3 μm obtained in <Pulverization ofpositive electrode active material particles> described above.

<Preparation of Coated Negative Electrode Active Material Particles(B-3)>

An amount of 90 parts by weight of non-graphitizable carbon [availablefrom Kureha Battery Materials Japan Co., Ltd., CARBOTRON (registeredtrademark) PS(F)] was put into a universal mixer. While stirring at 150rpm at room temperature, the coating resin solution (resin solidconcentration: 30% by weight) was added dropwise over 60 minutes suchthat the amount of resin solid added was 5 parts by weight. Theresulting mixture was further stirred for 30 minutes.

Subsequently, while stirring, 5 parts by weight of acetylene black[available from Denka Company Limited., DENKA BLACK (registeredtrademark)] was added to the mixture in three steps. The temperature wasraised to 70° C. while stirring for 30 minutes. The pressure was reducedto 0.01 MPa and the mixture was held for 30 minutes. In this manner,coated negative electrode active material particles (B-3) were obtained.

<Preparation of Coated Negative Electrode Active Material Particles(B-4)>

Coated negative electrode active material particles (B-4) were obtainedin the same manner as in the preparation of (B-3) except that the 90parts by weight of non-graphitizable carbon [available from KurehaBattery Materials Japan Co., Ltd., CARBOTRON (registered trademark)PS(F)] was changed to 90 parts by weight of the non-graphitizable carbonwith average particle size of 2.5 μm obtained in <Pulverization ofnegative electrode active material particles>described above.

<Preparation of Carbon Fibers (C)>

Carbon fibers (C) were prepared with reference to the method disclosedin Eiichi Yasuda, Asao Oya, Shinya Komura, Shigeki Tomonoh, TakashiNishizawa, Shinsuke Nagata, Takashi Akatsu, CARBON, 50, 2012, pp.1432-1434 and Eiichi Yasuda, Takashi Akatsu, Yasuhiro Tanabe, KazumasaNakamura, Yasuto Hoshikawa, Naoya Miyajima, TANSO, 255, 2012, pp.254-265.

An amount of 10 parts by weight of synthetic mesophase pitch AR⋅MPH[available from Mitsubishi Gas Chemical Company, Inc.] as a carbonprecursor and 90 parts by weight of polymethylpentene TPX RT18[available from Mitsui Chemicals, Inc.] were melt-kneaded at a barreltemperature of 310° C. under nitrogen atmosphere using a single-screwextruder. Thus, a resin composition was prepared.

The resin composition was melt-extruded and spun at 390° C. The spunresin composition was put in an electric furnace and held at 270° C.under nitrogen atmosphere for three hours, so that the carbon precursorwas stabilized. Subsequently, the temperature of the electric furnacewas raised to 500° C. over one hour and the spun composition was held at500° C. for one hour, so that the polymethylpentene was decomposed andremoved. The temperature of the electric furnace was raised to 1000° C.over two hours, and the remaining stabilized carbon precursor was heldat 1000° C. for 30 minutes, so that it was converted into conductivefibers.

An amount of 90 parts by weight of the obtained conductive fibers, 500parts by weight of water, and 1000 parts by weight of zirconia balls (Φ0 0.1 mm) were put into a pot mill and the conductive fibers werepulverized for five minutes. The zirconia balls were removed byclassification and then the conductive fibers were dried at 100° C.Thus, conductive carbon fibers (C) were obtained.

Measurement with a SEM showed that the fibers had an average fiberdiameter of 0.9 μm and an average fiber length of 25 μm.

<Preparation of Electrolyte Solution>

LiPF₆ was dissolved in a mixed solvent of ethylene carbonate (EC) anddiethyl carbonate (DEC) (volume ratio: 1:1) at 1 mol/L. Thus, anelectrolyte solution for lithium ion batteries was prepared.

Example 1

Urethane foam that was nickel-plated and thus provided with conductivity[available from Seiren, Co., Ltd., Sui-70-5005, thickness: 450 μm,electrical conductivity: 300 mS/cm] was provided. The urethane foam is astructure (Z) including a resin provided with conductivity as aconductive member (A), has a large number of voids, and has a first mainsurface and a second main surface.

Separately, 85.5 parts by weight of LiCoO₂ powder [available from NipponChemical Industrial Co., Ltd., CELLSEED C-8G] as positive electrodeactive material particles and 4.75 parts by weight of acetylene black[available from Denka Company Limited., DENKA BLACK (registeredtrademark)] were mixed with a solution of 4.75 parts by weight ofpolyvinylidene fluoride (available from Sigma-Aldrich) inN-methylpyrrolidone (hereinafter NMP). Thus, a solvent slurry wasprepared.

The solvent slurry in such an amount that the weight of the componentsin the solvent slurry other than NMP was 95 parts by weight was appliedto one main surface of 5 parts by weight of the urethane foam.Pressurization from above the surface with the solvent slurry wasperformed at a pressure of 2.0 kg/cm², so that the voids in the urethanefoam were filled with the positive electrode active material particles.Thereafter, the workpiece was dried at 80° C. for 120 minutes at normalpressure to remove the solvent, and then dried at 80° C. for eight hoursunder reduced pressure. Thus, a positive electrode for lithium ionbatteries was prepared.

Example 2

The coated positive electrode active material particles (B-1) were mixedwith the above electrolyte solution to prepare an electrolyte solutionslurry.

An amount of 5 parts by weight of the same urethane foam as that inExample 1 was provided. The electrolyte solution slurry in such anamount that the weight of the coated positive electrode active materialparticles was 95 parts by weight was applied to one main surface of theurethane foam. Pressurization from above the surface with theelectrolyte solution slurry was performed at a pressure of 1.5 kg/cm²,so that the voids in the urethane foam were filled with the coatedpositive electrode active material particles. Thus, a positive electrodefor lithium ion batteries was prepared.

Example 3

An amount of 90 parts by weight of the coated positive electrode activematerial particles (B-1) and 5 parts by weight of acetylene black[available from Denka Company Limited., DENKA BLACK (registeredtrademark)] were mixed with the above electrolyte solution to prepare anelectrolyte solution slurry.

An amount of 5 parts by weight of the same urethane foam as that inExample 1 was provided. The electrolyte solution slurry in such anamount that the weight of the components in the electrolyte solutionslurry other than the electrolyte solution was 95 parts by weight wasapplied to one main surface of the urethane foam. Pressurization fromabove the surface with the electrolyte solution slurry was performed ata pressure of 1.5 kg/cm², so that the voids in the urethane foam werefilled with the coated positive electrode active material particles.Thus, a positive electrode for lithium ion batteries was prepared.

Table 1 shows the electrode composition, the thickness, the proportionsby volume of the conductive member (A) and the active material (B), andthe weight per unit area of the positive electrodes for lithium ionbatteries prepared in Examples 1 to 3.

TABLE 1 Electrode composition (wt %) Electrode Conductive Pro- Pro-member Active Con- portion by portion by Weight Discharge (A) materialductive volume of volume per capacity Ni- (B) additive conductive ofactive unit per weight plated Coated Acety- Thick- member material areaof active urethane LCO Binder lene ness (A) (B) (mg/ material (mAh/g)foam LCO (B-1) PVdF black (μm) ( vol %) (vol %) cm²) 0.1 C 0.2 C 0.5 C1.0 C Example 1 5 85.5 — 4.75 4.75 500 12 48 120 153 154 123 69 Example2 5 — 95 — — 500 12 48 120 138 115 85 34 Example 3 5 — 90 — 5 500 12 51120 151 145 108 53 In the table, LCO refers to LiCoO₂ particles. CoatedLCO refers to coated LiCoO₂ particles.

Example 4

Carbon fiber-made nonwoven fabric [available from Osaka Gas ChemicalsCo., Ltd., DONACARBO Paper S-253, thickness: 650 μm, electricalconductivity: 400 mS/cm] was provided. The nonwoven fabric is astructure (Z) including a conductive member (A) made of conductivefibers, has a large number of voids, and has a first main surface and asecond main surface. Hereinafter, the nonwoven fabric is referred to asa nonwoven fabric A.

Separately, 88 parts by weight of LiCoO₂ powder [available from NipponChemical Industrial Co., Ltd., CELLSEED C-8G] and 5 parts by weight ofacetylene black [available from Denka Company Limited., DENKA BLACK(registered trademark)] were mixed with a solution of 5 parts by weightof polyvinylidene fluoride (available from Sigma-Aldrich) in NMP. Thus,a solvent slurry (C) was prepared.

The solvent slurry in such an amount that the weight of the componentsin the solvent slurry other than NMP was 98 parts by weight was appliedto one main surface of 2 parts by weight of the nonwoven fabric A.Pressurization from above the surface with the solvent slurry wasperformed at a pressure of 2.0 kg/cm², so that the voids in the nonwovenfabric A were filled with the positive electrode active materialparticles. Thereafter, the workpiece was dried at 80° C. for 120 minutesat normal pressure to remove the solvent, and then dried at 80° C. foreight hours under reduced pressure. Thus, a positive electrode forlithium ion batteries was prepared.

Example 5

The same electrolyte solution slurry as that in Example 2 was prepared.

An amount of 2 parts by weight of a nonwoven fabric A, which was thesame as that in Example 4, was provided. The electrolyte solution slurryin such an amount that the weight of the coated positive electrodeactive material particles (B-1) was 98 parts by weight was applied toone surface of the nonwoven fabric A. Pressurization from above thesurface with the electrolyte solution slurry was performed at a pressureof 1.5 kg/cm², so that the voids in the nonwoven fabric A were filledwith the coated positive electrode active material particles. Thus, apositive electrode for lithium ion batteries was prepared.

Example 6

Carbon fiber-made nonwoven fabric [available from Osaka Gas ChemicalsCo., Ltd., DONACARBO Paper S-259P, thickness: 500 μm, electricalconductivity: 500 mS/cm] was provided. The nonwoven fabric is astructure (Z) including a conductive member (A) made of conductivefibers, has a large number of voids, and has a first main surface and asecond main surface. Hereinafter, the nonwoven fabric is referred to asa nonwoven fabric B.

A positive electrode for lithium ion batteries was prepared in the samemanner as in Example 4 except that the nonwoven fabric A was changed tothe nonwoven fabric B.

Example 7

A positive electrode for lithium ion batteries was prepared in the samemanner as in Example 5 except that the nonwoven fabric A was changed tothe nonwoven fabric B.

Table 2 shows the electrode composition, the thickness, the proportionsby volume of the conductive member (A) and the active material (B), andthe weight per unit area of the positive electrodes for lithium ionbatteries prepared in Examples 4 to 7.

TABLE 2 Electrode composition (wt %) Electrode Conductive Pro- Pro-member Active Con- portion by portion by Weight Discharge (A) materialductive volume of volume per capacity Non- Non- (B) additive conductiveof active unit per weight woven woven Coated Acety- Thick- membermaterial area of active fabric fabric LCO Binder lene ness (A) (B) (mg/material (mAh/g) A B LCO (B-1) PVdF black (μm) ( vol %) (vol %) cm²) 0.1C 0.2 C 0.5 C 1.0 C Example 4 2 — 88 — 5 5 490 4 45 120 152 151 138 124Example 5 2 — — 98 — — 510 4 59 120 142 112 42 19 Example 6 — 2 88 — 5 5480 4 62 120 154 151 135 122 Example 7 — 2 — 98 — — 500 4 58 120 147 12453 21 In the table, LCO refers to LiCoO₂ particles. Coated LCO refers tocoated LiCoO₂ particles.

Example 8

Carbon fibers [available from Osaka Gas Chemicals Co., Ltd., DONACARBOChop S-231, average fiber length: 3300 μm, average fiber diameter: 13μm, electrical conductivity: 200 mS/cm] were provided as a conductivemember (A). Hereinafter, the carbon fibers are referred to as carbonfibers A.

An amount of 1.75 parts by weight of the carbon fibers A and 98.25 partsby weight of the coated positive electrode active material particles(B-1) were mixed with the above electrolyte solution to prepare anelectrolyte solution slurry.

A stainless steel mesh [available from Sunnet Industrial Co., Ltd.,SUS316 twilled dutch weave, 2300 mesh] was provided as a film (E). Theelectrolyte solution slurry was applied to the stainless steel mesh andthen subjected to suction-filtration (depressurization), so that thecoated positive electrode active material particles and the carbonfibers were fixed onto the stainless steel mesh. Thus, a positiveelectrode for lithium ion batteries was prepared.

Example 9

The electrolyte solution slurry of the positive electrode for lithiumion batteries prepared in Example 8 was further pressurized at apressure of 1.5 kg/cm². Thus, a positive electrode for lithium ionbatteries was prepared.

Example 10

Carbon fibers [available from Osaka Gas Chemicals Co., Ltd., DONACARBOMilled S-243, average fiber length: 500 μm, average fiber diameter: 13μm, electrical conductivity: 200 mS/cm] were provided as a conductivemember (A). Hereinafter, the carbon fibers are referred to as carbonfibers B.

An amount of 1.75 parts by weight of the carbon fibers B and 98.25 partsby weight of the coated positive electrode active material particles(B-1) were mixed with the above electrolyte solution to prepare anelectrolyte solution slurry.

The same stainless steel mesh as that in Example 8 was provided as afilm (E). The electrolyte solution slurry was applied to the stainlesssteel mesh, and then subjected to suction-filtration (depressurization)while pressurizing at 1.5 kg/cm², so that the coated positive electrodeactive material particles and the carbon fibers were fixed onto thestainless steel mesh. Thus, a positive electrode for lithium ionbatteries was prepared.

Examples 11 and 12

A positive electrode for lithium ion batteries was prepared in the samemanner as in Example 10 except that the amount of electrolyte solutionslurry applied was smaller than in Example 10 to reduce the thickness ofthe electrode.

Example 13

A positive electrode for lithium ion batteries was prepared by peelingthe fixed electrode from the stainless steel mesh in Example 12.

Example 14

A mixed powder was prepared by dry-mixing 1.75 parts by weight of thecarbon fibers B and 98.25 parts by weight of the coated positiveelectrode active material particles (B-1). The mixed powder was spreadon a metal plate (iron plate) and leveled with an applicator.Thereafter, the powder was hot-pressed at 180° C. and 1.5 MPa for oneminute. Thus, an electrode for lithium ion batteries was obtained inwhich the carbon fibers and the (coated) positive electrode activematerial particles were fixed by a coating resin.

The electrode was peeled from the iron plate and subjected to adischarge capacity evaluation.

Example 15

The carbon fibers (C) (average fiber length: 25 μm, average fiberdiameter: 0.9 μm, electrical conductivity: 30 mS/cm) prepared in<Preparation of Carbon fibers (C)>, described above, were provided as aconductive member (A). Hereinafter, the carbon fibers are referred to ascarbon fibers C.

An amount of 1 part by weight of the carbon fibers C and 99 parts byweight of the coated positive electrode active material particles (B-2)were mixed with the above electrolyte solution to prepare an electrolytesolution slurry.

The same stainless steel mesh as that in Example 8 was provided as afilm (E). The electrolyte solution slurry was applied to the stainlesssteel mesh, and then subjected to suction-filtration (depressurization)while pressurizing at 1.5 kg/cm², so that the coated positive electrodeactive material particles and the carbon fibers were fixed onto thestainless steel mesh. The electrode was then peeled from the mesh. Thus,a positive electrode for lithium ion batteries was prepared.

Examples 16 and 17

A positive electrode for lithium ion batteries was prepared in the samemanner as in Example 15 except that the proportions of the carbon fibersC and the coated positive electrode active material particles (B-2) werechanged as shown in Table 3, and that the amount of the electrolytesolution slurry applied was changed to adjust the thickness of theelectrode.

Examples 18 and 19

A positive electrode for lithium ion batteries was prepared in the samemanner as in Example 15 except that the pressure applied in thepressurization, which was 1.5 kg/cm² in Example 15, was changed. Thepressure was 4.0 kg/cm² in Example 18 and 35 kg/cm² in Example 19.

Examples 20 to 23

A positive electrode for lithium ion batteries was prepared in the samemanner as in Example 15 except that the carbon fibers C and the coatedpositive electrode active material particles (B-2) were used as shown inTable 3, and that the amount of the electrolyte solution slurry appliedwas changed to adjust the thickness of the electrode.

Table 3 shows the following properties of the positive electrodes forlithium ion batteries prepared in Examples 8 to 23: the electrodecomposition, the thickness, the proportions by volume of the conductivemember (A) and the active material (B), the total length of carbonfibers as the conductive member (A) per unit volume of the electrode[expressed as “Total fiber length (cm/cm³) of conductive member (A)” inthe table], and the weight per unit area of the electrode.

The thickness of the positive electrode for lithium ion batteriesexcludes the thickness of the film (E) in Examples 8 to 13 and 15 to 23and excludes the thickness of the iron plate in Example 14.

TABLE 3 Electrode composition (wt %) Conductive Active member (A)material (B) Conductive Carbon Carbon Carbon Coated Coated additivefibers fibers fibers LCO LCO Binder Acetylene A B C LCO (B-1) (B-2) PVdFblack Example 8 175 — — — 98.25 — — — Example 9 175 — — — 98.25 — — —Example 10 — 1.75 — — 98.25 — — — Example 11 — 1.75 — — 98.25 — — —Example 12 — 1.75 — — 98.25 — — — Example 13 — 1.75 — — 98.25 — — —Example 14 — 1.75 — — 98.25 — — — Example 15 — — 1 — — 99 — — Example 16— — 3 — — 97 — — Example 17 — — 5 — — 95 — — Example 18 — — 1 — — 99 — —Example 19 — — 1 — — 99 — — Example 20 — — 1 — — 99 — — Example 21 — — 1— — 99 — — Example 22 — — 1 — — 99 — — Example 23 — — 1 — — 99 — —Electrode Pro- Pro- Total portion portion by fiber by Discharge volumeof length of volume capacity conductive conductive of active Weight perweight Thick- member member material per unit of active ness (A) (A) (B)area material (mAh/g) (μm) ( vol %) (mg/cm²) (vol %) (mg/cm²) 0.1 C 0.2C 0.5 C 1.0 C Example 8 570 6 12,092 45 120 150 142 74 32 Example 9 5006 13,785 51 120 153 151 100 63 Example 10 500 6 13,785 51 120 160 158134 105 Example 11 400 6 14,359 53 100 160 160 139 117 Example 12 250 613,785 51 60 161 160 155 124 Example 13 250 6 13,785 51 60 160 159 152116 Example 14 250 6 13,785 51 60 152 133 71 35 Example 15 470 22,158,627 55 120 160 159 155 145 Example 16 500 6 6,212,841 51 120 160158 146 128 Example 17 605 10 8,737,794 47 120 160 157 143 112 Example18 410 2 2,481,180 63 120 160 157 145 121 Example 19 365 2 2,840,299 72120 160 156 139 125 Example 20 705 2 2,158,627 55 180 160 159 155 145Example 21 1128 2 2,158,627 55 288 160 141 125 101 Example 22 2350 22,158,627 55 600 150 123 98 65 Example 23 4700 2 2,158,627 55 1200 145120 85 35 In the table, LCD refers to LiCoO₂ articles. Coated LCD refersto coated LiCoO₂ particles

Example 24

The same urethane foam as that in Example 1 was provided as a structure(Z).

Separately, 80.75 parts by weight of non-graphitizable carbon [availablefrom Kureha Battery Materials Japan Co., Ltd., CARBOTRON (registeredtrademark) PS(F)] as negative electrode active material particles wasmixed with a solution of 4.25 parts by weight of polyvinylidene fluoride(available from Sigma-Aldrich) in NMP. Thus, a solvent slurry wasprepared.

The solvent slurry in such an amount that the weight of the componentsin the solvent slurry other than NMP was 85 parts by weight was appliedto one main surface of 15 parts by weight of the urethane foam.Pressurization from above the surface with the solvent slurry wasperformed at a pressure of 2.0 kg/cm², so that the voids in the urethanefoam were filled with the negative electrode active material particles.Thereafter, the workpiece was dried at 80° C. for 120 minutes at normalpressure to remove the solvent and then dried at 80° C. for eight hoursunder reduced pressure. Thus, a negative electrode for lithium ionbatteries was prepared.

Example 25

An amount of 76.5 parts by weight of non-graphitizable carbon [availablefrom Kureha Battery Materials Japan Co., Ltd., CARBOTRON (registeredtrademark) PS(F)] as negative electrode active material particles and4.25 parts by weight of acetylene black [available from Denka CompanyLimited., DENKA BLACK (registered trademark)] were mixed with a solutionof 4.25 parts by weight of polyvinylidene fluoride (available fromSigma-Aldrich) in NMP. Thus, a solvent slurry was prepared.

The solvent slurry in such an amount that the weight of the componentsin the solvent slurry other than NMP was 85 parts by weight was appliedto one main surface of 15 parts by weight of the urethane foam.Pressurization from above the surface with the solvent slurry wasperformed at a pressure of 2.0 kg/cm², so that the voids in the urethanefoam were filled with the negative electrode active material particles.Thereafter, the workpiece was dried at 80° C. for 120 minutes at normalpressure to remove the solvent and then dried at 80° C. for eight hoursunder reduced pressure. Thus, a negative electrode for lithium ionbatteries was prepared.

Example 26

The coated negative electrode active material particles (B-3) were mixedwith the above electrolyte solution to prepare an electrolyte solutionslurry.

An amount of 15 parts by weight of the same urethane foam as that usedin Example 24 was provided. The electrolyte solution slurry in such anamount that the weight of the coated negative electrode active materialparticles was 85 parts by weight was applied to one main surface of theurethane foam. Pressurization from above the surface with theelectrolyte solution slurry was performed at 1.5 kg/cm², so that thevoids in the urethane foam were filled with the coated negativeelectrode active material particles. Thus, a negative electrode forlithium ion batteries was prepared.

Example 27

An amount of 80 parts by weight of the coated negative electrode activematerial particles (B-3) and 5 parts by weight of acetylene black[available from Denka Company Limited., DENKA BLACK (registeredtrademark)] were mixed with the above electrolyte solution to prepare anelectrolyte solution slurry.

An amount of 15 parts by weight of the same urethane foam as that inExample 24 was provided. The electrolyte solution slurry in such anamount that the weight of components in the electrolyte solution slurryother than the electrolyte solution was 85 parts by weight was appliedto one surface of the urethane foam. Pressurization from above thesurface with the electrolyte solution slurry was performed at 1.5kg/cm², so that the voids in the urethane foam were filled with thecoated negative electrode active material particles. Thus, a negativeelectrode for lithium ion batteries was prepared.

Table 4 shows the following properties of the negative electrodes forlithium ion batteries prepared in Examples 24 to 27: the electrodecomposition, the thickness, the proportions by volume of conductivemember (A) and the active material (B), and the weight per unit area ofthe electrode.

TABLE 4 Electrode composition (wt %) Con- Electrode ductive Pro- Pro-member Active Con- portion by portion Weight Discharge (A) materialductive volume of by volume per capacity Ni- (B) additive conductive ofactive unit per weight plated Coated Acety- Thick- member material areaof active urethane HC Binder lene ness (A) (B) (mg/ material (mAh/g)foam HC (B-3) PVdF black (μm) ( vol %) (vol %) cm²) 0.1 C 0.2 C 0.5 C1.0 C Example 24 15 80.75 — 4.25 — 700 12 51 61 420 415 370 220 Example25 15 76.5 — 4.25 4.25 700 12 50 59 425 420 405 250 Example 26 15 — 85 —— 700 12 50 60 371 363 251 169 Example 27 15 — 80 — 5 700 12 50 59 402395 367 182 In the table, HC refers to non-graphitizable carbonparitcles. Coated HC refers to coated non-graphitizable carbonparitcles.

Example 28

The same carbon fibers B as those in Example 10 were provided as aconductive member (A).

An amount of 4.2 parts by weight of the carbon fibers B and 95.8 partsby weight of the same non-graphitizable carbon as that in Example 24 asnegative electrode active material particles were mixed with the aboveelectrolyte solution. Thus, an electrolyte solution slurry was prepared.

An aramid separator (available from Japan Vilene Company, Ltd.) wasprovided as a film (E). The electrolyte solution slurry was applied tothe separator and subjected to suction-filtration (depressurization)while pressurizing at 1.5 kg/cm², so that the negative electrode activematerial particles and the carbon fibers were fixed onto the aramidseparator. Thus, a negative electrode for lithium ion batteries wasprepared.

Examples 29 and 30

A negative electrode for lithium ion batteries was prepared in the samemanner as in Example 28 except that the amount of the electrolytesolution slurry applied was smaller than in Example 28 to reduce thethickness of the electrode.

Example 31

A negative electrode for lithium ion batteries was prepared in the samemanner as in Example 28 except that 95.8 parts by weight of the coatednegative electrode active material particles (B-3) were used as negativeelectrode active material particles instead of 95.8 parts by weightnon-graphitizable carbon.

Examples 32 and 33

A negative electrode for lithium ion batteries was prepared in the samemanner as in Example 31 except that the amount of the electrolytesolution slurry applied was smaller than in Example 31 to reduce thethickness of the electrode.

Example 34

The same carbon fibers C as those in Example 15 were provided as aconductive member (A).

A negative electrode for lithium ion batteries was prepared in the samemanner as in Example 28 except that 4.2 parts by weight of the carbonfibers C were used as the conductive member (A) instead of the carbonfibers B, and that 95.8 parts by weight of the coated negative electrodeactive material particles (B-3) were used as the negative electrodeactive material particles instead of 95.8 parts by weight ofnon-graphitizable carbon.

Examples 35 to 37

A negative electrode for lithium ion batteries was prepared in the samemanner as in Example 34 except that the coated negative electrode activematerial particles (B-4) were used instead of the coated negativeelectrode active material particles (B-3), and that the proportions ofthe carbon fibers C and the coated negative electrode active materialparticles (B-4) were changed as shown in Table 5.

Examples 38 to 40

A negative electrode for lithium ion batteries was prepared in the samemanner as in Example 35 except that the carbon fibers C and the coatednegative electrode active material particles (B-4) were used as shown inTable 5, and the amount of the electrolyte solution slurry applied waschanged to adjust the thickness of the electrode.

Example 41

In Example 35, the obtained electrolyte solution slurry was applied tocopper foil with a thickness of 20 μm thick as a current collector,instead of an aramid separator. After the application, an aramidseparator was disposed on the slurry, followed by pressurization fromthe upper surface of the separator at 1.5 kg/cm², so that liquid exudedfrom the upper surface of the separator. The liquid was absorbed. Thus,a negative electrode for lithium ion batteries containing a currentcollector was prepared.

Table 5 shows the following properties of the negative electrodes forlithium ion batteries prepared in Examples 28 to 41: the electrodecomposition, the thickness, the proportions by volume of the conductivemember (A) and the active material (B), the total fiber length of carbonfibers as a conductive member (A) per unit volume of the electrode[expressed as “Total fiber length (cm/cm³) of conductive member (A)” inthe table], and the weight per unit area of the electrode.

TABLE 5 Electrode composition (wt %) Con- ductive Conductive Activeaddi- member (A) material (B) tive Electrode Carbon Carbon Coated CoatedAcety- Thick- fibers fibers HC HC Binder lene ness B C HC (B-3) (B-4)PVdF black (μm) Example 28 4.2 — 95.8 — — — — 880 Example 29 4.2 — 95.8— — — — 650 Example 30 4.2 — 95.8 — — — — 390 Example 31 4.2 — — 95.8 —— — 880 Example 32 4.2 — — 95.8 — — — 690 Example 33 4.2 — — 95.8 — — —410 Example 34 — 4.2 — 95.8 — — — 500 Example 35 — 2 — — 98 — — 490Example 36 — 4.2 — — 95.8 — — 500 Example 37 — 6 — — 94 — — 520 Example38 — 2 — — 98 — — 980 Example 39 — 2 — — 98 — — 2450 Example 40 — 2 — —98 — — 3920 Example 41 — 2 — — 98 — — 490 Electrode Pro- Pro- portionportion by Total fiber by volume of length of volume conductiveconductive of active Weight Discharge member member material percapacity per weight (A) (A) (B) unit area of active material (mAh/g) (vol %) (mg/cm²) (vol %) (mg/cm²) 0.1 C 0.2 C 0.5 C 1.0 C Example 28 1.510,107 45 67 401 387 294 164 Example 29 1.5 10,211 45 50 407 391 346 194Example 30 1.5 10,211 45 30 415 408 387 358 Example 31 1.5 11,230 45 67399 374 284 257 Example 32 1.5 10,688 46 50 397 382 326 297 Example 331.5 10,793 46 30 397 385 374 341 Example 34 1.5 3,155,817 48 43 410 391341 261 Example 35 1.5 1,499,014 48 43 405 395 364 346 Example 36 1.53,155,817 46 43 400 394 381 362 Example 37 1.5 4,417,922 45 43 397 385364 342 Example 38 1.5 1,499,014 48 86 370 335 285 228 Example 39 1.51,499,014 48 215 358 310 251 192 Example 40 1.5 1,499,014 48 344 335 284231 145 Example 41 1.5 1,499,014 48 43 410 397 371 348 In the table, HCrefers to non-graphtizable carbon paritcles. Coated HC refers to coatednon-graphitzable carbon paritcles

Comparative Example 1

An amount of 90 parts by weight of LiCoO₂ powder [available from NipponChemical Industrial Co., Ltd. CELLSEED C-8G] as positive electrodeactive material particles and 5 parts by weight of acetylene black[available from Denka Company Limited., DENKA BLACK (registeredtrademark)] were mixed with a solution of 5 parts by weight ofpolyvinylidene fluoride (available from Sigma-Aldrich) in NMP. Thus, asolvent slurry was prepared.

The solvent slurry was applied to one surface of aluminum electrolyticfoil having a thickness of 20 μm with a wire bar in the air. The slurrywas dried at 100° C. for 15 minutes. Thus, a positive electrode forlithium ion batteries of Comparative Example 1 was prepared.

Comparative Example 2

An amount of 95 parts by weight of non-graphitizable carbon [availablefrom Kureha Battery Materials Japan Co., Ltd., CARBOTRON (registeredtrademark) PS(F)] as negative electrode active material particles wasmixed with a solution of 5 parts by weight of polyvinylidene fluoride(available from Sigma-Aldrich) in NMP. Thus, a solvent slurry wasprepared.

The solvent slurry was applied to one surface of copper foil having athickness of 20 μm with a wire bar in the air. The workpiece was driedat 80° C. for three hours at normal pressure and then vacuum-dried at80° C. for eight hours to evaporate the solvent. Thus, a negativeelectrode for lithium ion batteries of Comparative Example 2 wasprepared.

Table 6 shows the following properties of the positive electrode andnegative electrode prepared in Comparative Examples 1 and 2: theelectrode composition, the thickness, the proportions by volume of theconductive member (A) and the active material (B), and the weight perarea of the electrode.

TABLE 6 Electrode Electrode composition (wt %) Pro- Pro- Con- portion byportion Weight Discharge ductive volume of by volume per capacity Activeadditive conductive of active unit per weight Conductive material Acety-Thick- member material area of active member (B) Binder lene ness (A)(B) (mg/ material (mAh/g) (A) LCO HC PVdF black (μm) ( vol %) (vol %)cm²) 0.1 C 0.2 C 0.5 C 1.0 C Comparative — 90 — 5 5 400 0 55 120 124 9431 14 Example 1 Comparative — — 95 5 — 600 0 55 67 270 243 114 35Example 2 In the table, LCO refers to LiCoO₂ particles. HO refers tonon-graphitizable carbon particles.

[Preparation of Lithium Ion Battery for Evaluating Positive Electrode]

Each of the positive electrodes prepared in Examples 1 to 23 andComparative Example 1 was punched into a size of 17 mmφ. The punched-outelectrode and a negative electrode made of Li metal having a size of 17mmφ were disposed at both ends inside a 2032 type coin cell.

Aluminum electrolytic foil having a thickness of 20 μm was used as acurrent collector on the positive electrode side. In the case of thepositive electrodes of Examples 8 to 12, which were fixed onto stainlesssteel mesh, the stainless steel mesh was located on the currentcollector side.

Two separators (Celgard 3501) were interposed between the electrodes.Thus, a cell for lithium ion batteries was prepared. The aboveelectrolyte solution was poured into the cell, and the cell was sealed.The discharge capacity (mAh) was measured by the method below. Theresulting value was divided by the weight of the active material, andthe discharge capacity (mAh/g) per weight of the active material wasevaluated.

[Preparation of a Lithium Ion Battery for Evaluating Negative Electrode]

Each of the negative electrodes prepared in Examples 24 to 41 andComparative Example 2 was punched into a size of 17 mmφ. The punched-outelectrode and a positive electrode made of Li metal having a size of 17mmφ were disposed at both ends inside a 2032 type coin cell.

Copper foil having a thickness of 20 μm was used as a current collectoron the negative electrode side. In the case of the negative electrodesof Examples 28 to 40, in which an aramid separator was used, the aramidseparator was located on the separator side (positive electrode side).

In the case of the negative electrode of Example 41, which wasintegrated with a current collector and a separator, copper foil as acurrent collector was not used and the aramid separator was located onthe separator side (positive electrode side).

Two separators (Celgard 3501) were interposed between the electrodes.Thus, a cell for lithium ion batteries was prepared. The aboveelectrolyte solution was poured into the cell, and the cell was sealed.The discharge capacity (mAh) was measured by the method below. Theresulting value was divided by the weight of the active material, andthe discharge capacity (mAh/g) per weight of the active material wasevaluated.

<Evaluation of Discharge Capacity of Lithium Ion Battery>

Using a charge/discharge measuring apparatus “Battery analyzer Model1470” [available from TOYO Corporation], the batteries were each chargedat 0.1 C, 0.2 C, 0.5 C, or 1.0 C at room temperature. The batteries forevaluating a negative electrode were charged until the voltage reached2.5 V and the batteries for evaluating a positive electrode were chargeduntil the voltage reached 4.3 V. After a 10-minute rest, the batterieswere discharged at 0.1 C, 0.2 C, 0.5 C, or 1.0 C. The batteries forevaluating a negative electrode were discharged until the voltagereached 10 mV and the batteries for evaluating the positive electrodewere discharged until the voltage reached 2.7 V, and the batterycapacity was measured.

Tables 1 to 6 show the discharge capacity (mAh/g) per weight of activematerial in the examples and the comparative examples.

The electrodes for lithium ion batteries according to the examples, evenones having an increased thickness, had excellent electricalconductivity. It was found that higher discharge capacity per weight ofthe active material was exhibited despite the increased thickness. Theelectrode of the present invention can be used as an electrode forlithium ion batteries excellent in the discharge capacity per unit area.

INDUSTRIAL APPLICABILITY

The electrode for lithium ion batteries according to the presentinvention is particularly useful as an electrode for, for example,bipolar secondary batteries and lithium ion secondary batteries forcellular phones, personal computers, hybrid automobiles, and electricvehicles.

REFERENCE SIGNS LIST

-   Lithium ion battery 1-   Electrode (positive electrode) for lithium ion batteries 10, 110,    210, 210′, 310-   First main surface of positive electrode 11, 111, 211, 311-   Second main surface of positive electrode 12, 112, 212, 312-   Conductive fiber constituting part of nonwoven fabric 13,-   13 a, 13 b-   Positive electrode active material particles 14-   Coating agent 15, 25-   Conductive additive 16, 26-   Electrode (negative electrode) for lithium ion batteries 20, 220-   First main surface of negative electrode 21, 221-   Second main surface of negative electrode 22, 222-   Negative electrode active material particles 24-   Separator 30-   Current collector 40, 50-   Nonwoven fabric (structure) 60-   Second main surface of nonwoven fabric 62-   Filter paper 70, 470-   Conductive fiber constituting part of woven fabric 113-   Warp yarn 113 a-   Weft yarn 113 b-   Conductive fiber dispersed between first main surface and second    main surface 213, 213 a, 213 b, 223-   Resin 214-   Slurry layer 225-   Resin provided with conductivity 313-   Plate 570

1-22. (canceled)
 23. A method of producing an electrode for lithium ionbatteries, the electrode comprising: a first main surface to be locatedadjacent to a separator of a lithium ion battery; and a second mainsurface to be located adjacent to a current collector of the lithium ionbattery, wherein the electrode contains, between the first main surfaceand the second main surface, a conductive member (A) made of anelectronically conductive material, a large number of active materialparticles (B), and a resin (F), at least part of the conductive member(A) forms a conductive path that electrically connects the first mainsurface to the second main surface, and the conductive path is incontact with the active material particles (B) around the conductivepath, and the conductive member (A) comprises conductive fibers, themethod comprising step (R1) of hot-pressing a composition for anelectrode containing the conductive member (A), the active materialparticles (B), and the resin (F) so as to fix the conductive member (A)and the active material particles (B) by the resin (F).
 24. (canceled)